The present invention relates to a method of producing a packaging container with low bacteria contamination.
Packaging containers of single-use disposable type are employed for packing different types of consumer products, e.g. foods such as milk or juice. In such instance, use is normally made of packaging containers which have been manufactured from a laminated material comprising layers of paper and thermoplastic, and possibly additional layers of metal foil or some other barrier material, e.g. barrier plastic. The packaging containers are manufactured in that the packaging laminate, in web or sheet form, is reformed into hose or tube form, provided with a first end closure seal and filled with the desired contents, being finally sealed at the other end.
Packaging containers of the above-mentioned or similar type are used, for example, for packing pasteurised milk. The filled and sealed package must, in this instance, be stored in cold storage, for example at a maximum temperature of +8xc2x0 C. and will then have a shelf life of 6 to 8 days. This shelf life is generally sufficient in the packing of perishable goods and in handling in an existing, unbroken refrigeration chain, i.e. immediate cooling after filling and sealing, transport in refrigerated vehicles and exposure for sale in refrigerated display counters.
When the intention is to pack milk or other food products so that they obtain a longer shelf life and/ or can be handled and transported without the requirement of refrigeration, use is made of so-called aseptic packaging containers which, prior to filling with the desired contents, are subjected to a bactericidal treatment. In this instance, for example a chemical sterilisation agent may be used, such as hydrogen peroxide (H2O2) or the packaging container may also be subjected to some form of irradiation sterilisation, for example in that its interior is illuminated with UV light of suitable, bactericidal wavelength (combinations of other methods may possibly also be employed). When a thus treated packaging container is ready for filling with its contents, the bacterial contamination level has been reduced to such an extent that no growth of bacteria can thereafter take place, naturally on condition that the contents have also been sterilised beforehand, for example by heat treatment to such a temperature that the contents are in practice bacteria-free. When the thus treated packaging container, under sterile conditions, has been filled with the sterile contents and sealed, the package will have a shelf life of several months; in certain cases, for example in the packing of less sensitive products such as, for instance, orange juice, a shelf life of up to a year. Moreover, this shelf life will be obtained without any demands needing to be placed on cold storage or handling of the package under special conditions.
In recent years, aseptic packages produced in the above-outlined manner for, for instance, dairy produce have enjoyed increasing expansion in use, in particular in countries wherexe2x80x94because of the climate and level of developmentxe2x80x94it is not possible to ensure that the packages can be handled and stored under refrigerated conditions. However, the sterilising treatment of both the packaging containers and their contents renders production more complicated and more expensive, and since it has proved in practice that, in many countries, only a fraction of the maximum shelf life is used, there has arisen a need for a package which, from the point of view of shelf life, is an intermediate stage between the original, unsterile packaging container type for pasteurised contents and the aseptic package displaying extremely long shelf life. This compromise, which makes for a slightly longer shelf life than non-aseptic packages but, at the same time, may be produced employing considerably less of a technical input and at a considerably lower cost, is normally entitled xe2x80x9cextended shelf lifexe2x80x9d (ESL). Such a package is subjected to a limited, bacteria-reducing treatment and is filled with contents which are not sterile, but handled under such safety regulations that the bacteria contamination is extremely low. In such instance, it is possible to achieve a shelf life of 4 to 6 weeks (depending on the product), on condition that the packaging container is handled in the refrigerated state.
In the prior art production of packaging containers of this ESL type, a bacteria-reducing treatment of the packaging container takes place without achieving the level of sterility which is the case in so-called aseptic packaging containers. In the treatment of, for example, a packaging material web, it will here be possible, on the one hand, to carry out more rapid treatment, and on the other hand to reduce the input as regards, for example, the concentration of the sterilisation agent employed (hydrogen peroxide) or the time for the irradiation treatment in irradiation sterilisation as compared with that which is required for producing an aseptic package of the above-mentioned type. In the bacteria-reducing treatment of already partly finished packaging containers, for example the type of packaging container which is described in European Patent Specification 217.282, it has, however, in practice proved to require a relatively long time, or alternatively sterilisation agent at a high concentration in order to ensure a satisfactory level of bacteria destruction. The design of, for example, the bottom of the packaging container with a plurality of partly overlapping, folded wall sections gives uneven, complicated forms and pockets adjacent the folding and sealing regions which are difficult to sterilise with the desired outcome. However, it has here proved that the gain which could theoretically be attained by reducing the requirements from the level stipulated for the production of aseptic packaging containers to the level which is necessary for the production of xe2x80x9cextended shelf lifexe2x80x9d packaging containers cannot be achieved in practice. As a result, the advantages in prospect will not materialise, since, for example, a more highly concentrated chemical sterilisation agent will also be more difficult to remove and thereby requires higher temperatures and/or longer times to ensure low residual quantities, which is a manifest disadvantage also from the point of view of energy and economics. Since all of these drawbacks are related to the presence of pockets and mutually overlapping material areas, in particular at the bottom region of the packaging container, it would appear that the sought-for advantages could be attained if only the packaging design and construction is such that the bottom of the packaging container becomes more planar and free from concealed areas, and is preferably also produced in such a manner that the bacteria contamination or loading will be relatively slight already from the outset.
One object of the present invention is to realise a method of producing a packaging container with low bacteria contamination, the method making it possible to simplify and speed up the bacteria-reducing treatment of the packaging container.
A further object of the present invention is to realise a method of producing a packaging container with low bacteria contamination, the method realising a packaging container of such construction and configuration that the bacteria-reducing treatment may be made both simpler and quicker than has hitherto been the case.
Yet a further object of the present invention is to realise a method of producing a packaging container, the method of production having been adapted and optimised in order to simplify the subsequent, bacteria-reducing treatment of the interior of the packaging container.
Still a further object of the present invention is, finally, to realise a method of producing a packaging container with low bacteria contamination, the method both simplifying and economising the production of the finished packaging container and obviating the drawbacks inherent in prior art methods.